A motorist travelingalong a straight portion of a highway is decreasing the speed of his automobile at a constant rate before existing from the highway into a circular exit ramp with a radius of 560-ft. he continue to decelerate at the same constant rate so that 10s after entering the ramp, his speed has decreased to 20mi/h, a speed which he then maintains. Knowing that at this constant speed the total acceleration of the automobile is equal to one-quarter of its value prior to entering the ramp, determine the maximum value of the total acceleration of the automobile.